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IC 883? 



Bureau of Mines Information Circular/1981 



^^^/(fixA 




Noise Control of Diesel-Powered 
Underground Mining Machines, 1979 



Compiled by J. H. Daniel, J. A. Burks, 

R. C. Bartholomae, R. Madden, and E. E. Ungar 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Ksj&cO JUtcfaj. &tA&*<*-> tf y?fao^. 



Information Circular 8837 



Noise Control of Diesel-Powered 
Underground Mining Machines, 1979 



Compiled by J. H. Daniel, J. A. Burks, 

R. C. Bartholomae, R. Madden, and E. E. Ungar 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 



if 



/ A/z?f 



This publication has been cataloged as follows: 



Noise control of diesel-powered underground mining 


machines, 


1979. 




(Information circular - Bureau of Mines ; 8837) 




Includes bibliographies- 




Supt. of Docs, no.: I 28-27:8837- 




1. Mining machinery— Noise- 2- Diesel motor— Noise- 


3- Noise- 


Physiological effect- I. Daniel, J. H. II. Series: United 


States- Bu* 


reau of Mines- Information circular ; 8837- 




TN295.U4 [TN345] 622s [622'.2l 8O607181 





CONTENTS 



Page 



Abs tract 1 

Introduction 1 

Federal noise regulations 2 

Machinery noise levels and worker exposure 3 

Machine types and numbers in use 3 

Noise doses and expo sure -weigh ted worker population 4 

Noise control 5 

General principles 5 

Importance of attenuating dominant contributions 5 

Major sources and paths 7 

Reduction of noise of diesel-powered equipment 7 

Airborne paths 7 

S tructureborne paths 8 

Machines quieted 8 

Personnel vehicle 9 

Source levels 9 

Engine enclosure 10 

Acoustically absorptive lining 11 

Hole and crack sealing 12 

Intake, fan, and exhaust noise 13 

Results 15 

Service experience 15 

Load -haul -dump machine 16 

Noise reduction package 17 

Drive train 17 

Engine 22 

Cooling fan 26 

Results 28 

Service experience 28 

Conclusions 29 

ILLUSTRATIONS 

1 . Getman dispatch vehicle . . . , 9 

2. Sketch of removable partial engine enclosure 10 

3. Removable panel for partial enclosure 11 

4. Acoustic adsorption treatments 12 

5. Examples of sealed holes and voids, operator vicinity 13 

6 . Fan inlet modifications to prevent recirculation 14 

7. Fan inlet configuration 14 

8. Getman dispatch operator sound level--before and after quieting.... 15 

9 . Load -haul-dump machine 16 

10 . Transmission compartment cover 18 

11. Transmission hood vibration isolation 19 

12. Transmission front cover 20 

13. Acoustical treatment for interior of fuel and water tank 

compartment 21 



XI 



ILLUS TRATIONS - - Continued 

Page 

14 . Torque converter cover 21 

15. Absorptive materials applied to the interior of the torque 

converter compartment 22 

16. Transmission vibration isolation mounting structure 23 

17 . Engine enclosure , external view 23 

18. Components of engine enclosure 24 

19. Belly pan with cooling fan exhaust duct lining 25 

20. Stiffening applied to engine frame rail 26 

21. Baffle in lowered (left) and raised (right) positions 27 

22. Quieted machine, shown underground at National Gypsum Mine 28 

23. Comparison of above ground and underground sound pressure levels 

measured on load-haul-dump machines 28 

TABLES 

1. Permissible noise exposures 3 

2. Numbers of machines found in use, by type and engine power 4 

3. Typical worker-machine scenarios for noise impact over an 8-hour 

shift 6 

4. Source levels on the Getman dispatch vehicle 10 

5 . Source levels on the Wagner load -haul-dump machine 16 



NOISE CONTROL OF DIESEL-POWERED UNDERGROUND 
MINING MACHINES, 1979 

Compiled by 

J. H. Daniel, ] J. A. Burks, 2 R. C. Bartholomae, 3 R. Madden, 4 and E. E. Ungar 4 



ABSTRACT 

This Bureau of Mines report presents results of a survey of underground 
mining equipment and of two demonstration programs showing the feasibility of 
quieting a load-haul-dump (LHD) machine and a personnel vehicle. Typical 
noise levels are presented for the major machine types used in underground 
mines, along with estimates of the noise overexposure of miners who operate 
or work near these machines. General principles of noise control are 
explained, and the application of these principles is illustrated in the 
description of modifications made to the LHD machine and the personnel vehi- 
cle. The noise control package installed on the personnel vehicle lowered its 
noise level by 14 dBA after 4 months of operation, and inspection of the LHD 
machine after 2% years of operation with the modifications showed its noise 
level 7 dBA lower than that of the unmodified machine. Noise dosimeter meas- 
urements indicated that both machines were in compiliance with Federal noise 
regulations for a typical shift. 

INTRODUCTION 

A great many machines currently used in underground metal and nonmetal 
mines are powered by diesel engines, which often produce relatively high 
levels of noise. Because Federal regulations limit the permissible noise 
exposure of personnel, the Bureau of Mines has sponsored studies to assess the 
noise exposure of workers from diesel-powered equipment and to demonstrate 
that engineering noise control of these machines is feasible. 



1 Program manager, Branch of Health Research, Bureau of Mines, Washington, D.C. 
-Technical Project Officer, Pittsburgh Research Center, Bureau of Mines, 

Pittsburgh, Pa. 
Supervisory electrical engineer, Pittsburgh Research Center, Bureau of Mines, 

Pittsburgh, Pa. 

4 

^Bolt, Beranek and Newman Inc. , Cambridge, Mass. 

5 Federal Mine Safety and Health Act of 1977 (Public Law 95-164). 



This Information Circular summarizes the results of a survey of mining 
equipment and two demonstration programs that demonstrate the feasibility of 
quieting a load-haul-dump machine and a personnel vehicle. Details of each 
of these programs are available. 

FEDERAL NOISE REGULATIONS 

Miners are not usually exposed to the same noise level continuously; most 
commonly they experience noise levels that change throughout the working day. 
Since higher noise levels constitute more of a hearing hazard than lower ones, 
the effects of these different levels must be accounted for. The "noise dose" 
is a standard measure that accomplishes this accounting and also relates a 
worker's total noise exposure to the permissible limit. 

Federal regulations permit a worker to be exposed to a noise level of 
90 dBA for 8 hours per day and prescribe a halving of the permissible expo- 
sure time for each 5-dBA increase in noise level, as shown in table 1. 

A miner who is exposed for C hours per day to a noise level for which 
the permitted exposure duration is T hours is considered to be subjected to a 
noise dose of C/T because of this exposure. Thus, a noise dose that exceeds 
1.0 represents an excessive exposure, whereas a noise dose of less than 1.0 
corresponds to an exposure that is within the permissible limits. 



6 The following reports are available from the National Technical Information 
Service/ (NTIS) , Springfield, Va. (order by PB number) and for inspection 
(on open file) at the following facilities: Bureau of Mines— Denver , Colo. , 
Twin Cities, Minn. , Bruceton and Pittsburgh, Pa. , and Spokane, Wash. ; 
U.S. Dept. of Energy — Carbondale, 111., and Morgantown, W. Va. ; National 
Mine Health and Safety Academy, Beckley, W. Va. ; and National Library of 
Natural Resources, U.S. Dept. of the Interior, Washington, D. C. 

Huggins, G. G. , R. Madden, and B. S. Murray. Noise Control of an Underground 
Load-Haul-Dump Machine. BuMines Open File Rept. 125-78, July 1977, 79 pp. , 
contract HO262013; NTIS, PB 288 854/AS. 

Huggins, G. G. , and W. N. Patterson. Reducing the Operator Sound Level of a 
Mining Service Vehicle — A Demonstration Project. BuMines Open File Rept. 
47-77, November 1975, 75 pp.; contract HO346046; NTIS PB 265 037/AS. 

Patterson, W. N. , G. G. Huggins, and A. G. Galaitsis. Noise of Diesel- 
Powered Underground Mining Equipment. Impact, Prediction, and Control. 
BuMines Open File Rept. 58-75, March 1975, 227 pp. ; contract HO346046; 
NTIS, PB 243 896/AS. 



TABLE 1 . - Permissible noise exposures 



Duration of exposure per day, hours 


Noise level, 


dBA 


8 


90 

92 

95 

97 

100 

102 

105 

110 

115 




6 




4 




3 




2 




1.5 




1 




0.5 




0.25 





NOTE. --Noise levels are measured with a sound level 
meter set to slow response. Exposure to con- 
tinued levels above 115 dBA is not permitted. 
Values between those tabulated may be obtained 
from 

T = __§___,- 



2(L-90)/5 

where T denotes the daily exposure duration in 
hours and L the noise level in dBA. 

If a miner is exposed to different noise levels throughout the day, one 
may evaluate the miner's total noise dose simply by adding up all of the C/T 
values corresponding to the various noise levels. Commercially available 
instruments called noise dosimeters perform this dose evaluation automatically 
and continuously. 

MACHINERY NOISE LEVELS AND WORKER EXPOSURE 
Machine Types and Numbers in Use 

Discussions in 1975 with the regional offices of the Mine Safety and 
Health Administration, with State mining inspectors, and with major under- 
ground mine operators revealed that 2,638 specific pieces of diesel-powered 
equipment were being used in underground metal and nonmetal mines. This sur- 
vey did not cover all mines in the United States; however, extrapolation of 
the survey data leads to an estimate of about 4,000 for the total number of 
items in use. Table 2, which shows the distribution of the machines counted 
in the survey by type and engine power, indicates that more than 507 o of these 
machines had less than 100 hp and that load -haul -dump machines, ore trucks, 
and service trucks were the most prevalent. 

7 For example, a person exposed to 90 dBA for 6 hours, to 100 dBA for 1 hour, 
and to 70 dBA for 1 hour per day receives a dose of (6/8) + (1/2) + = 
1.25, and thus is overexposed. Similarly, a person exposed to 97 dBA for 
1/4 hour, 95 dBA for 2 hours, 90 dBA for 3 hours per day, and to noise 
levels less than 90 dBA for the remainder of the working day receives a 
dose of (0.25/3) + (2/4) + (3/8) + = 0.958, and thus is not overexposed. 



TABLE 2. - Numbers of machines found in use, 
by type and engine power 



Types of equipment 


Under 100 hp 


100-200 hp 


Over 200 hp 


Total 


Production machines: 

Load-haul-dumps 


227 

147 

44 

112 

67 

32 

29 

12 

31 

1 




66 

190 

97 

33 

11 

20 

14 

24 



8 

6 


172 
49 
45 
4 





5 
8 


465 
386 


Front-end loaders 


186 


Jumbo drills 

Locomotives 


149 

78 


Roof bolters and scalers 

Shuttle cars 


52 
43 


Explosive buggies 


36 


Ram haulers 


31 

14 


Tractor-trailer units 


14 


Total 


702 


469 


283 


1,454 






Support Equipment: 

Personnel carriers 


187 
199 
132 

76 

35 

14 

6 

8 

5 

10 

6 

6 

2 


16 
2 

3 

16 
17 
4 
1 
1 
3 




2 


1 


1 
5 
9 
1 





205 
201 


Tractors 


132 
80 


Transit mixers and placers. . . . 
Motor graders 


35 

30 


Dozers 


24 
17 


Air compressors 


15 


Shotcrete machines 


12 
9 

6 




2 


Total 


686 


63 


19 


768 




165 


170 


81 


416 


Total 


1,553 


702 


383 


2,638 







Noise Doses and Exposure-Weighted Worker Population 

Table 3 indicates the noise dose to which each type of machine typically 
subjects each operator and bystander. For each machine type, table 3 shows 
the typical engine power and the corresponding average noise levels at full 
speed (noisiest) operating conditions. The table also shows the fraction of 
its operating time during which a machine typically is used in its noisiest 
mode, and the fraction during which it is used in its next noisiest mode 
(called "reduced speed" in the table and assumed to be 5 dBA quieter than the 
full speed mode). For the remainder of the time, the machine is assumed to 



be used in a mode of operation that makes no contribution to the noise expo- 
sure of the workers. This time fraction information and the estimated total 
number of hours a machine is in use per shift, together with the aforementioned 
noise levels, permit one to estimate noise doses to which the machines subject 
nearby personnel. 

Also shown in table 3 are the numbers of operators and bystanders who 
usually work with each machine and the estimated number of machines in use. 
By adding, for a given machine type, the product of the number of operators 
and the operator noise dose to the product of the number of bystanders and the 
bystander noise dose, one finds the "exposure-weighted number of workers" for 
that machine. If one multiplies this number by the number of machines in use, 
one obtains the "expo sure -weigh ted population of workers" associated with that 
machine. The latter is a convenient measure of the noise exposure impact 
related to the given type of machine. 

One may conclude from table 3 that ore trucks and load-haul-dump machines 
have the predominant impact on personnel exposure, with personnel carriers, 
front-end loaders, service trucks, tractors, locomotives, shuttle cars, and 
air compressors (in that order) contributing to a lesser extent. 

The estimates shown in table 3 do not account for a worker's being exposed 
to noise from more than one machine at a time. Although two or more machines 
often are used in conjunction with each other, their operations usually are 
cyclic, so that only one is operating at its noisiest part of the cycle at any 
instant. Also, the nearest machine usually dominates a worker's exposure, so 
that neglecting the effects of the nearby machines results in errors in the 
exposure estimates that are smaller than those inherent in the data on which 
these estimates are based; thus, no significant error results from neglecting 
the effects of simultaneous exposure to more than one machine. 

NOISE CONTROL 

General Principles 

Importance of Attenuating Dominant Contributions 

In general, the noise from any one source reaches a person's ears via 
several paths, both direct airborne paths and reflections from various sur- 
faces; in addition, sound may propagate along or through structures (in the 
form of vibrations) . Just as repair of small holes in a leaking roof is use- 
less unless the large holes are closed off, reducing the noise of lesser 
sources and paths has practically no effect on a person's exposure unless the 
contributions from the dominant sources and paths are reduced. 



8 An alternate method of obtaining noise dose data directly is to use a sta- 
tistically significant sample of noise dosimeter data. 



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Major Sources and Paths 

In diesel-powered mining equipment, the engine generally constitutes a 
major source of noise. Engine noise may come from the exhaust, the intake, 
and the casing (that is, the block and accessories attached to it); also, the 
cooling fan may be a significant noise source. The transmission, drive train, 
and hydraulic system also tend to be significant noise sources. 

Noise radiated from the various sources may reach the operator by propa- 
gation through the air, either directly or via reflections. In addition, 
vibrations produced by the engine and other mechanical components tend to 
travel through heavy structures, such as frame rails, to lighter structures 
that then radiate sound somewhat in the manner of a loudspeaker. 

The relative importance of the various noise sources and paths differs 
for different machine types and models. 

Reduction of Noise of Diesel-Powered Equipment 

In general, the noise exposure of a miner associated with a given machine 
may be reduced by obstructing the sound propagation between the important noise 
sources and the worker. Practical and economical considerations generally do 
not permit one to modify the primary noise sources or to replace them with 
quieter ones (except relatively early in the development cycle of new machines), 
Consequently, practical reduction of the noise of machines in use at mines gen- 
erally has obstruction of the propagation paths as its first concern. 

As mentioned previously, sound for a given source may reach a miner by 
propagation through the air, including reflections, and also by propagation 
along and through structures. Thus, one must deal with blocking the airborne 
paths and also the structural paths. 

Airborne Paths 

Full enclosures generally are the most efficient for obstructing the radia- 
tion of sound from such sources as engines or transmissions. The effective- 
ness of such an enclosure increases with the mass of its walls, and it is 
greater if some acoustically absorptive material is also placed within the 
enclosure. 

Where cooling or access requirements do not permit the use of complete 
enclosures, partial enclosures or barriers may be used. These tend to be 
considerably less effective than full enclosures, because they do not inter- 
fere with sound that is propagating in directions away from them or past their 
ends and that may then be reflected in the direction of concern. The effec- 
tiveness of a partial enclosure or barrier may be enhanced by placing 
acoustically absorptive material on the sides that face the noise sources. 
Because the noise reduction one obtains with a partial enclosure or barrier 
usually is not limited by the sound that passes through it, but by the sound 
that gets around it, increasing the barrier or enclosure mass (which reduces 
the sound passing through these structures) usually results in little addi- 
tional noise reduction. 



Mufflers are devices that obstruct the propagation of sound out of pipes 
or ducts, largely by reflecting some of the sound back toward the sources in 
such a way that the reflected pressure waves cancel the outgoing waves to a 
considerable extent. Engine exhaust mufflers must be matched to the engine 
so as to be effective accoustically, yet not produce excessive backpressure. 

Like mufflers, silencers obstruct the propagation of sound out of pipes 
or ducts (for example, out of air intakes). However, silencers work not by 
reflecting sound internally, but by absorbing sound. Thus, silencers gener- 
ally consist of acoustically lined pipes or ducts with baffles or louvers 
of acoustically absorptive material inside them. Silencers generally must be 
selected to provide the desired sound attenuation without excessive obstruc- 
tion of air flow. 

Structureborne Paths 

The propagation of vibrations along structures (vibrations that may cause 
structural surfaces to radiate sound in loudspeaker like fashion) usually may 
be obstructed efficiently by inserting vi'brat'ion- / isolation elements into the 
propagation path. Such elements typically need to be much softer than the 
structure they join; they may consist of rubber mounts placed between a vibrat- 
ing engine or transmission and its supports or of flexible hose inserted in 
a run of rigid hydraulic tubing. 

The remainder of this Information Circular discusses how these basic 
principles were applied to the noise control of two machines identified in the 
survey to be major contributors to the noise overexposure problem in under- 
ground metal and nonmetal mines. 

MACHINES QUIETED 

Diesel-powered machinery used in mines can be divided into two broad 
categories: loading/hauling equipment and service vehicles. Machines in both 
categories are noisy and numerous. The 1975 census showed that 2,200 loaders- 
haulers were being used in U.S. mines, and that 690 were load-haul-dump vehi- 
cles. Service vehicles--a term that covers all vehicles used to move personnel 
and equipment (lube trucks, maintenance vehicles, explosive trucks, drill 
carriers, and any vehicle that carries personnel are included) --ran a close 
second: 1,800 were in mines in 1975. The Bureau of Mines selected one machine 
from each of these categories for a demonstration of noise control feasibility. 
One was a load-haul -dump (LHD) machine, the other a personnel vehicle. 

Sound levels of both machines categories are high. Typical sound levels 
on LHD machines, measured at the operator's ear, reach 100 dBA. The average 
sound level of service vehicles is 96 dBA. 




FIGURE 1. - Getman dispatch vehicle. 



Personnel Vehicle 

A three-passenger 
Getman dispatch vehicle 
(fig. 1) was used in the 
noise control demonstration. 
This vehicle has two models , 
the other carrying 12 pas- 
sengers. Both models are 
the same size; the extra 
space on the three-passenger 
vehicle is used for material 
handling or as a portable 
maintenance -service facility. 



The vehicles are 18 ft 
long, with a wheelbase some- 
what over 9 ft. Power is 
supplied by a 45-hp, four- 
cylinder Deutz air-cooled 
diesel engine (Model F4L- 
912W) through a four-speed 
manual transmission. Body metal is primarily 1/4-inch steel plate. The 
engine is located immediately to the operator's left, and, in the unquieted 
vehicles, the engine is fully exposed. 

Because of the exposed engine and the operator's closeness to it, the 
sound level at the operator's ear is considerably higher than in most service 
vehicles of similar horsepower. The measured sound level was 101 dBA at high 
idle, compared with an average 96' dBA for similar machines given in table 3. 

Source Levels 

Four different sources of noise contribute to the 101-dBA sound level at 
high idle of Getman dispatches : 

• Engine. 

• Intake. 

• Cooling fan. 

• Exhaus t . 

Measurements and diagnoses of these sources of noise indicating their 
levels are shown in table 4. The engine, then was by far the largest con- 
tributor to the total noise of the dispatch vehicle, with the intake and 



9 Reference to specific makes or models of equipment is made for identification 
only and does not imply endorsement by the Bureau of Mines. 



10 



cooling fan about equal in contribution and the exhaust relatively unimpor- 
tant. 1 A noise control package was designed that included: 

Engine : 

• A barrier or partial enclosure around the engine. 

• An acoustically absorbent lining for the interior of the engine 

compartment. 

• Sealing for all holes and cracks in the engine enclosure. 

Intake: 

• Installation of a silencer in the intake line. 
Muffler: 

• Asbestos wrapping for the muffler shell. 

TABLE 4. - Source levels on the Getman 





dispatch vehicle 


Source 


Level, dBA 


Test condition 


Fan 


100 
89 
90 

<80 


>High idle. 




- 



The fan received no specific noise control, because the enclosures would 
reduce fan, as well as engine noise. 

Engine Enclosure 

The engine partial 
enclosure is shown in fig- 
ures 2 and 3. It is con- 
structed of 1/8-inch-thick 
sheet metal. 

The larger door (approx- 
imately 6 -inch -square) pro- 
vides access to the oil 
dipstick (fig. 3B) , and the 
smaller door provides access 
to the oil filler cap (fig. 
3C) . Gasket stripping was 
used on the edges of all 
panels , doors , and cover 
plates to ensure a tight seal. 




FIGURE 2. - Sketch of removable partial engine enclosure. 



10 The contribution of the 
exhaust is low because 
the dispatch comes 
equipped with an exhaust 
muffler. 



11 






FIGURE 3. - Removable panel for partial enclos- 
ure. A, Enclosure; B, oil dipstick 
access; C, oil filler access. 



Although the prototype enclosure was bolted to the Getman dispatch, 
similar enclosures could be attached by quick-release fasteners to cut down 
maintenance time . 

Acoustically Absorptive Lining 

The engine compartment of the Getman dispatch was lined with acous- 
tically absorptive materials — fiberglass and polyure thane foam 11 in equal 
parts--to prevent the sound level from building up because of repeated reflec- 
tions of noise within the engine space. 

In addition, plastic foam was applied to the underside of the canopy, 
over the operator's head. These treatments are illustrated in figure 4. The 
film-wrapped fiberglass was held to the surface of the machine by the expanded 
grating, which in turn was bolted to the machine. 



i:L Although the polyurethane foam does meet the acoustic requirements, it has 
an exceptionally high flame spread index and emits toxic fumes when burned. 
It is therefore recommended that future treatments use more suitable mate- 
rials, such as fiberglass. 



12 






FIGURE 4. - Acoustic adsorption treatments. A, 
Fiberglass under engine head; B, 
foam in rear engine compartment; C , 
foam under operator canopy. 



Hole and Crack Sealing 

Great care was taken to seal all holes and cracks in the structure 
around the operator to make sure no engine noise would leak through. Figure 5 
illustrates this meticulous sealing, including: 

• A rubber boot around the shift lever. 

• A steel cover plate bolted over a hole in the panel to the operator's 

immediate left. 



• A cover plate over a hole on the rear of the transmission and battery 
compartment. 

In general, any opening one-fourth inch or larger was considered a "hole", 
and was sealed with a steel plate to which gasket stripping had been applied. 



13 



Boot around 
gear shift 



Battery 

compartment 

covered 




Gap in rear 
of panel 
sealed 



Hole on operator's 
left sealed 

FIGURE 5. - Examples of sealed holes and voids, operator vicinity. 

Intake, Fan, and Exhaust Noise 

To cut air intake noise, a standard cylindrical silencer was installed 
between the air cleaner and the engine. This installation involved moving 
the filter a few feet toward the rear of the vehicle and bolting the air 
cleaner to the frame. The muffler was wrapped with asbestos. 

Since air recirculation within the enclosure could cause overheating, a 
metal panel and cowling were installed on the front of the engine hood. As 
figure 6 shows, cooling air entered the fan opening front, passed by the 
cylinder fins, and exited to the left of the engine. Components of the fan 
inlet are shown in figure 7 . 



14 



Entering 
cool air 



Metal panel to prevent 
recirculation (dashed arrow) 




Exiting warm air 



FIGURE 6. - Fan inlet modifications to prevent recirculation. 



Existing 

fan 

cowling 



Rubber 

transition 

piece 




FIGURE 7. - Fan inlet configuration. 



15 



Results 

When it was completely installed, the noise control package — engine 
enclosure, acoustically absorbent lining in the engine compartment, sealing, 
intake silencer, and asbestos wrapping of the muffler — cut the noise of the 
Getman dispatch by 14 dBA. Without the quieting package, the overall sound 
level of the dispatch was measured as 101 dBA; after quieting, it was meas- 
ured as 87 dBA. Figure 8 shows spectra recorded before and after the treat- 
ment. Measurements in both cases were taken to the right of the operator's 
right ear, with the engine at high idle. 

Service Experience 

Four months after the Getman dispatch had been put in service at 
International Salt's Detroit Mine, the vehicle had been used for 60 to 70 
hours and had received typical periodic maintenance (engine oil change, fil- 
ter changes, tuneup, etc.). There had been no noticeable change in the acous- 
tics of the dispatch; it was as quiet as when the noise reduction package was 
first applied. 

Mine workers said they preferred to drive the demonstration vehicle 
"because it was quieter." They suggested that quick-release fasteners be 
applied to the partial enclosure, which must be removed for preventive mainte- 
nance every 3 months or whenever repairs are made on the engine. 



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FIGURE 8. - Getman dispatch operator sound level— before and after quieting. 



16 




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FIGURE 9. - Load-haul-dump machine. 



Load -Haul -Dump Machine 

The Wagner ST-5A Scooptram (fig. 9) is one of the most widely used load- 
haul-dump (LHD) machines in underground mining. It is a low-profile loader, 
67 inches high, with a 5-cu-yd bucket mounted on the front. Just to the rear 
of the bucket is the center-articulated steering wheel, which allows short- 
radius turns in mines. The driver sits at the side of the aft section of the 
vehicle, facing inward, since the vehicle has the same tram capabilities in 
either forward or reverse. Also located on the aft section is the air-cooled 
diesel engine, the torque converter, and the transmission. 

The diesel engine of the ST-5A is a Deutz 8-cylinder Model F8L-714, rated 
by the Bureau of Mines at 180 hp at 2,300 rpm. A single-stage Clark Model 
C-8402 torque converter is connected directly to the engine. A shaft from the 
torque converter drives the 4-speed Clark Model 3421 transmission, which in 
turn drives the front and rear differentials . 

Major sources of noise were-- 

• Drive train. 

• Engine. 

• Cooling fan. 

• Intake and exhaust. 

Measurements of these sources of noise indicating their levels (at the opera- 
tor's ear) are shown in table 5. 

TABLE 5. - Source levels on the Wagner 
load-haul-dump machine 



Source 


Level , 


dBA 


Test condition 


Drive train. 


101 
97 
94 
90 
93 


Rated speed in 4th gear. 




^High idle. 




Torque converter stall. 



17 



Noise Reduction Package 

Two noise sources--the intake and the exhaust--were eliminated from 
further consideration. The air intake was eliminated because its noise level 
was already low; the exhaust was eliminated because its principal contribu- 
tion was in the low-frequency range and because noise reduction would have 
required designing a completely new muffler. 

The drive train, engine, and fan were left as noise sources to be 
quieted. The package from them included: 

Drive train: 

• Sealing holes in operator compartment. 

• Transmission compartment cover. 

• Cover on water and fuel tank. 

• Acoustically absorbent lining in water and fuel tank compartment. 

• Acoustically absorbent lining in torque converter compartment. 

• Cover over torque converter. 

• Vibration isolation of transmission. 
Engine : 

• Enclosure. 

• Stiffening of frame rail. 
Cooling fan: 

• Baffle on grill. 

• Sealing of fan area. 

Drive Train 

The principal hole that needed sealing was around the steering column. 
It was sealed with a shroud with an elongated hole through which the steering 
column can pass and can also move to the three positions. The shroud was 
bolted through a gasket to the existing structure. 




FIGURE 10. - Transmission compartment cover. 



Covers (fig. 10) were installed around the transmission compartment. The 
interior surface was lined with 1-inch- thick 2-lb/cu-ft polyure thane foam 
with 0.0005-inch- thick aluminized Mylar facing. The facing was covered with 
a 22-gage (0.031-inch) perforated steel sheet with 51% open area. These 
layers were held together with studs welded to the cover plate and capped with 
washers and nuts . 

The transmission hood was vibration-isolated from the main structure of 
the LHD at the hinge by a rubber washer, as shown in figure 11. In addition, 
a rubber strip, 1/4 inch thick and 1 inch wide, was glued to the other three 
sides of the cover. 



19 



1/4" ID x 1/2" OD hose, 1/2" long 



1/4" UNC capscrew 

1/4" Flat washer 



1/8" thick x 1/2" IDx 1" OD 



Transmission 
hood 




1/8" thick x 2" x 32" rubber 
1/4" flat washer 
1/4" lock washer 

1/4" UNC nut 



FIGURE 11. - Transmission hood vibration isolation. 

The bottom of the transmission compartment was sealed with a belly pan 
made of 10-gage (0.139-inch) steel. A drain hole allowed transmission fluid 
to be emptied. 

Figure 12 shows the cover plate used to seal holes in the transmission 
compartment in the center, where the machine is pivoted. The cover was made 
of 10-gage steel and has 1/2 inch of polyurethane foam with 1/8-inch leaded 
rubber bounded to it. 

Another hole through which transmission noise leaked was the grate at 
the operator's feet. This was sealed by welding a plate underneath the 
grate. 

The water and fuel tank cover, noisy because of vibration, was quieted 
by adding a second cover. The second cover was vibration-isolated as shown 
in figure 13; it was made of 10-gage steel, with 1/2 inch of polyurethane 



20 




FIGURE 12. - Transmission front cover. 






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foam and 1/8-inch leaded rubber bonded to it for acoustical absorption and 
mass addition. 

The interior of the water and fuel tank compartment was treated with 
acoustical absorption material, as shown in figure 13. Approximately 14 sq ft 
of the 1-inch-thick Mylar-faced polyurethane foam was stud-welded to the front, 
back, and side surfaces. 

The torque converter was quieted with a 10-gage steel cover (fig. 14), to 
which 1-inch-thick Mylar-faced polyurethane foam was stud-welded. Large but- 
tons covered the studs and held the acoustical material in place. 

The interior of the torque converter compartment was lined with acousti- 
cal absorption material (fig. 15). Approximately 22 sq ft of the Mylar-faced 
polyurethane foam was stud-welded to the front, back, side, and top surfaces. 

Structureborne noise from the transmission was controlled by installing 
two Huntington M700 vibration mounts (nominal load capacity: 900 lb) on the 
transmission (weight: 1,100 lb), at the points where the transmission was 
hard -mounted to the main structure of the machine. The transmission vibration- 
isolation mounting strUc ture is shown in figure 16. 

Engine 

The diesel engine was quieted with an enclosure (fig. 17) that consisted 
of a hood, side panels, and belly pan with ducts for cooling air exhaust. 
Figure 18 shows the parts of the enclosure. When the air-cooled engine was 




FIGURE 15. - Absorptive materials applied to the interior of the torque converter 
compartment. 



23 




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24 





FIGURE 18. - Components of engine enclosure. A, Hood; B, left side enclosure; C, right side 
enclosure; I), belly pan and cooling air exhaust ducts. 



25 



enclosed, there is a potential for overheating. Cooling capacity was evalua- 
ted during two sets of experiments. A prototype enclosure with a lined 
exhaust duct was designed and built, then tested by noise control engineers 
and also by Deutz, the manufacturers of the engine. Both groups approved the 
enclosure design as having sufficient cooling capacity for the engine. 

The hood of the engine enclosure (fig. 18A) was made of 10-gage steel 
hinged to the main structure, with rubber gasketing material applied to the 
edges to vibration isolate it from the frame of the LHD. It was lined with 
1-inch- thick polyure thane foam with 0.0005-inch aluminized Mylar facing pro- 
tected by perforated steel. 

The left- and right-hand enclosures (figs. 18B and 18C) are also 10-gage 
steel with 2-inch- thick polyurethane foam with Mylar facing held on with studs 
and buttons . 

So that miners could reach the engine, the side enclosures were designed 
with removable sections attached to the fixed sections with hexhead bolts. 



Duct lining 




FIGURE 19. - Belly pan with cooling fan exhaust duct lining. 



26 



The belly pan and its cooling air exhaust ducts are shown in figure 18D. 
The pan was made of 5/8-inch-thick steel with two cutouts for exhausting the 
cooling air. The cutouts provided a total exhaust area of 4.7 sq ft. Fig- 
ure 19 shows the design of the lined ducts inside the engine enclosure. The 
ducts were made as separate pieces, were bolted to the belly pan, and were 
lined with 1-inch- thick , 2-lb/cu-ft polyurethane foam with 0.0005-inch 
aluminized Mylar protected by 22-gage perforated steel sheet. 

Structureborne noise from the engine was quieted by stiffening the frame 
rail. Triangular gussets, 6- by 6- by 1/2-inch, were welded to the ends of 
the frame rails, as shown in figure 20. 

Cooling Fan 

Figure 21 shows the treatments used to quiet the cooling fan. They 
included (1) sealing the entire area around the fan with 1-inch polyurethane 
foam with 0.0005-inch aluminized Mylar stud-welded to the structure and (2) 
placing a baffle on the fan grille. The baffle was covered with 1-inch 
polyurethane foam that "was covered, in turn, with 22-gage perforated steel 
plate. 



Engine frame rail 
3" x 3" x 1 / 2 " S\ 




Stiffening gusset 
6" x 6" x y 2 " 



FIGURE 20. - Stiffening applied to engine frame rail. 



27 




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FIGURE 22. - Quieted machine, shown underground at National Gypsum Mine. 



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1/3 Octave band center frequency, Hz 

IGURE 23. - Comparison of above ground and underground 
sound pressure levels measured on load-haul- 
dump machines. 



Results 

The quieted machine is 
shown (fig. 22) underground 
at the National Gypsum Mine 
in Shoals, Ind. A compari- 
son of the spectra measured 
aboveground before and after 
noise control is presented 
in figure 23. In all cases, 
the measurement was made 
near the operator's right 
ear with the engine at high 
idle. Noise dosimeter meas- 
urements made by the Mine 
Safety and Health Administra- 
tion (MSHA) indicate that 
the machine is in compliance 
when operated underground. 

Service Experience 

Sixty days after the 
machine was placed in ser- 
vice, a second, set of noise 



29 



measurements was made. There was no noticeable change in the acoustical per- 
formance of the machine. 

Mine employees reported that the noise control treatments were intact 
and performing as expected, indicating that the treatments were sufficiently 
practical for the use they underwent in the mine. A visit to the mine in 
March 1979 showed that all treatments are still intact after 2-1/2 years of 
service experience. Acoustical measurements at that time indicated no degrada- 
tion of the performance of the noise control. (As a result of this program, 
the manufacturer was encouraged to offer an optional quieting package at the 
time of purchase.) 

CONCLUSIONS 

The major contributors to the noise overexposure of underground metal 
and nonmetal miners by diesel-powered equipment were identified as load-haul- 
dump machines and ore trucks in the production category and personnel carriers 
in the support equipment category. The Bureau of Mines selected one piece of 
equipment from each of these categories for a demonstration of the feasibility 
of noise control. A load-haul-dump machine was selected to represent the pro- 
duction category; the model chosen, a Wagner ST-5A Scooptram , was quieted by 
7 dBA at the operator's position. The selected personnel carrier, an air- 
cooled Getman dispatch, was quieted by 14 dBA at the operator's position. 
Both machines were quieted to a point where they are in compliance with Fed- 
eral noise regulations for typical operations , and treatments on both machines 
are sufficiently durable to endure the mining environment. 

The techniques used in these demonstration programs are also applicable 
to the noise control of other diesel-powered underground mining machines. 
Mine personnel interested in implementing such noise control treatments on 
these machines or on others are encouraged to obtain copies of the contract 
reports (see footnote 6). 



irU.S. GOVERNMENT PRINTING OFFICE: 1981-703-002/02 int.-bu.of mines,pgh.,p a. 25163 



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